Process for the production of chemical wood pulp



.-'Patented May 7,. 1 929.

UNITED STATES.

PATEINTTTOFFICE.

:ooNAIai LB. BRADNER, or .mrmomoiaxo, ASSIGNOR TO 2cm: crmmrron coa'rnnimrnn so, or HAMILTO 01110, A CORPORATION or OHIO.

'P nocEssroa THE rnonuc'rron or Gunmen. woon P LP.

No Drawing.

This invention relates to an economical process of preparing a cellulosic pulp high in alpha cellulose content, and more particular;- ly to a process of treating sulfite pulp with alkaline liquors and using the waste liquors from said alkaline treatment in the preparation of a cooking liquor for a normal sulfate digestion of wood. I

Several processes have been proposed for the production of a wood pulp containing a high percentage of alpha cellulose, in which the wood is treated by a sulfite process to produce a sulfite pulp which is then treated with an'alkaline liquor. Presumably the secondary treatment with the alkaline liquor dissolves the degraded cellulose products, such as beta and gamma cellulose, and certain other materials of a non-cellulosic character which are not completely attacked by the sulfite cooking liquor. Usually this alkaline treatment is effected by sodium compounds,

such as for example,- sodium hydroxide or' sodium sulfide, In order that a wood pulping process involving the use of sodium compounds be economical it is necessary that a more or less complete recovery of the sodium compounds be accomplished. A number of processes have been described having for their particular object the economical recovcry of these valuable mineral constituents of spent cooking liquors. For example, according to one process heretofore disclosed, raw

cellulosic material is treated with an acid sul v fite cooking liquor to the production-of an unbleached pulp, the unbleached'pulp is separated and subsequently treated with a second cooking liquor comprising a soluble alkali (such as sodium carbonate, sodium sulfide, sodium hydroxide or caustic lime) ,-thereby producing a pulp having a high content of alpha cellulose,and the waste cooking liquor obtained as a by-p'roduct from said sec- 4 0nd treatment, with or without the addition of sodium carbonate or calcium carbonate is acidified with sulfur dioxide and reused as the acid sulfite cooking liquor in the primary digestion of raw cellulosic material. The said process avoids, the operations of evaporating, concentrating and smelting the waste alkaline cooking liquor of said seco pd digestion, which operations would otherwise be necessary in recovering the valuable constituents from said waste liquor. This process is open to the objection that more or less organic matter is precipitated when the spent Application filed January. 24, 1927 Serial No. 163,817. I

alkaline liquor is treated with sulfur dioxide.

This precipitated organic matter must be removed from the liquor before further use of the liquor. If the alkaline liquor used in this process contains sodium sulfide, sodium thio-sulfate isfcrmed upon the addition of sulfur dioxide, and this is detrimental to the acid sulfite process. On the other hand if the alkaline liquor contains no sodium sulfide, it .loses the advantages recognized as resulting.

from its use, and at the same time does not prevent the precipitation of organic matter when the spentliquors are treated with. sulf,ur dioxide.

i According'to another process wood is treated with an acid cooking liquorcontaining sodium sulfite andthe spent liquor neutralized, evaporated, the organic material burned and the resulting mass smelted in a reducing atmosphere to form sodium carbonate and sodium sulfide, which are then dissolved in water and used as an alkaline cookng liquor fora secondary treatment of the sulfite pulp previously produced. The spent alkaline liquors from this second digestion are next treated with carbon dioxide and then with sulfur dioxide to form an acid cooking liquor containing sodium sulfite-..

,The' carbon dioxide in the above process. displaces the hydrogen sulfide and conse quently avoids the formationof sodium thio- I sulfate. However, it does not-avoid the precipitation of organic matter when the sulfur dioxide is introduced.

According to the method which I have discovered, a wood pulp high in alpha cellulose I content can be economically produced which is free from the above described ,objections of preyiousprocesses.

v Wood or other,cellulosic material is first given a sulfite digestion. I prefenbut do not require that the mineral base for this sulfite digestion be sodium, rather than calcium or magnesium. The pulp resulting from this sulfite cook is separated from the spent liquor, whlch may be run. to waste or recovered. If

desired, the pulp, after washing, may now be given a bleachingtreatment, but this is not essential-to my invention.

The sulfite pulp is then digested with an alkaline liquor. This alkaline liquor is obtained from the waste liquor of anormal sulfate process by concentrating the waste liquor, burning the resulting concentrated product (containing considerable organic matter) and smelting the sodium compounds .thereof in a reducing atmosphere, thereby forming chiefly a mixture .of .sodium car-' bonate and sodium'sulfide, and dissolving or leaching the resulting smelted mixture in water; all as is done in standard practice.

The aqueous solution, or leach liquor, containing sodium carbonateand sodium sulfide, may then be causticized by treatment with caustic lime yielding an alkaline cooking 3 liquor comprising essentially sodiuin hydrox ideand sodium sulfide adaptedfor use directly in the heretofore described alkaline digestion of the sulfite pulp, or the saidaqueous solution may be used directly as the alkaline cooking liquor without causticization.

The digestion of the sulfite pulp with the above-described alkaline cooking liquor effects the solution of the residual lignin, resinous compounds, and the less stable celluloses from the sulfite pulp, to the production of a pulp having'a high content of alpha-cellulose and of a waste liquor that is used in the preparation of a cooking liquor for a normal sulfate process. t In the usual sulfate process, wood or other raw cellulosic materialg is digested with a solution containing caustic soda and sodium sulfide. After the digestion the pulp is separated from the liquor and washed, a certain amount of the wash water being added to the spent liquor. A part of this spent liquor together with some of the wash water is used directly as part of a cooking liquor for the next sulfate digestion of wood while the rest of'the spent liquor together with some of the wash water, is evaporated and the organic matter burned. The resulting mass is smelted in a reducing atmosphere yielding a mixture containing essentially sodium carbonate and sodium sulfide which is leached out with water and causticized with caustic lime to the production of sodium hydroxide and sodium sulfide for use in digesting a fresh charge of wood, or other cellulosic material. Due to various 1 losses of sulfur and sodium compounds it is necessary to add sodiumand sulfur at some point in the c cle and this is usually accomplished by adding crude sodium sulfate to the smelter. i

In my process I use the spent-liquors from the alkaline digestion of the sulfite pulp as make-up liquor for a sulfate digestion of wood, either directly or after causticization with caustic lime in the known manner. That is to say, in case the alkaline cooking liquor prepared from the smelt of thewaste sulfate liquor was causticized prior to its use in the alkaline digestion of sulfite pulp, the waste alkaline liquor from said alkaline digestion may be used directly in the preparation of a sulfate cooking liquor, whereas, in the event that causticization had not. been resorted to in the first instance, the waste alkaline liquor may be causticized by treatment with caustic lime-prior to its use as apart of the cooking liquor in the sulfate process. The presence of organic matter in solution therein is in no way detrimental to the sulfate digestion, and remains in solution until the waste sulfate liquor is smelted, where it has a distinct value as fuel.

These liquors from the-alkaline digestion of sulfite pulp contain a higher ratio of alkaline sodium compounds to dissolved organic matter than obtains in the spent liquors from a normal sulfate digestion of wood, because the liquors have been used for the digestion of pulp which-has already been freed to a considerable extent from lignin.

It is possible that these spent liquors resulting from the alkaline digestion of the sulfite pulp can be used as the entire cooking liquor for the collateral sulfate process without fortifying with recovered liquor, causticizing with lime in case uncausticized liquor was used in digesting the pulp, but I prefer to use the spent liquors from the alkalinedigestion of pulp simply as make-up liquor forLthe sulfate process.

Thespent liquors from the collateral sul- I fate treatment are evaporated, the organic matter burned, and the resulting mass smelted in a reducing atmosphere to the;formati0n of sodium sulfide and sodium carbonate which are then leached out with water. "This solution containing sodium sulfide and sodium carbonate is then used as the cooking liquor forlthe digestion of sulfite pulp causticizing if desired before digestion;

My process thus is seen to embrace the co-' operation of the known slil-fate process of making pulp with the process of making pulp of high alp a cellulose content involving the operations of digesting sulfite pulp either bleached or unbleached, with an alkaline cooking liquor comprising sodium hydroxide and sodium sulfide, saidoperation being characterized in that the alkaline liquor from the smelter of the collateral sulfate process is used as thealkaline cooking liquor for the digestion of the sulfite pulp,andthe waste alkaline liquor obtained as a by-product from the alkaline digestion of the sulfite pulp is used in the preparation of the cooking liquor in the sulfate process.

The particular advantages to be derived from the carrying out of my process are:

1. Complete washing of the sulfite pulp prior to digestion with-the alkaline cooking vantage that in case the valuable constituents of the sulfite liquors are to be recovered, there is no dilution of the spent liquors with wash water which would require additional evaporation. Also the valuable mineral constituents of the sulfite liquor which adhere to the sulfite pulp are not lost but are recovered in the recovery system of the collateral sulfate process.

3. The organic matter dissolved in the waste alkaline cooking liquor by-product fromthe alkaline digestion of sulfite pulp remains in solution throughout the sulfate cook and until the operation of smelting the residual waste liquor therefrom where it has a value as a fuel.

4. A distinct economy is effected by the use of the waste alkaline liquor as partof the cooking liquor in the collateral sulfate process of making pulp.

I claim:

1. Process of making chemical. wood pulp which comprises digesting raw cellulosic material in an acid cooking liquor comprising sodium sulfite, thereby forming sulfite pulp and waste sulfite'liquor, digesting the sulfite pulp in an alkaline cooking liquor containing sodium sulfide, forming thereby pulp havinga high content of alpha cellulose and waste alkaline liquor, and digesting raw cellulosic material in said waste alkaline liquor, forming thereby sulfate pulp and waste. sulfate liquor. t

2. Process of making chemical wood pulp which comprises digesting raw cellulosic material in an acid cooking liquor comprising sodium sulfite, thereby forming sulfite pulp and waste sulfite'liquor, digesting thesulfite pulp in an alkaline cooking liquor containing sodium sulfide, forming thereby pulp having a high content'of alpha cellulose and waste alkaline liquor, digesting raw cellulosic material in an alkaline liquor containing the said waste alkaline liquor, forming thereby sulfate pulp' and 'waste' sulfate liquor, concentrating the waste sulfate liquor, smelting and recovering therefrom the sodium compounds in aqueous solution and caustieizing said sodium compounds to the production of an alkaline cooking liquor, and using saidalkalme cooking liquor 1n the digestion of a further charge of sulfite pulp.

3. Process comprising the following steps: digesting sulfite pulp in an alkaline liquor containing sodium sulfide to the formation of a pulp having a high alpha cellulose content and waste alkaline liquor and using this waste alkaline liquor in the preparation of a cooking liquor for a sulfate digestion of wood.

4. Process comprising the following steps:

digesting sulfite pulp in an alkaline liquor containing sodium sulfide forming thereby pulp having a high content of alpha cellulose and waste alkaline liquor. digesting raw cellulosic material in an alkaline liquor containing the said waste alkaline liquor, form- "ing thereby sulfate pulp and waste sulfate liquor, concentrating the waste sulfate liquor, smelting and recovering therefrom the sodium compounds 1n"aqucous solution and causticizing the said sodium compounds to the production of an alkaline cooking liquor and using said alkaline cooking liquor in the digestion of a further charge of sulfite pulp.

5. The process of making chemical wood pulp having a high content of alpha cellulose involving the digestion of raw cellulosic material in an acid sulfite cooking l1quor, separation of the resulting waste sulfite liquor from the resulting sulfite pulp, and digestion "of the sulfite pulp in an alkaline cooking liquor; characterized in that the said alkaline cooking liquor is a solution comprising sodium sulfide obtained by concentrating smelting and recovering the sodium compounds present in the waste liquor from a collateral sulfate process of making pulp.

6. The process of making chemical wood pulp having a high content of. alpha cellulose involving thedigestion of raw cellulosic material in an acid sulfite cooking liquor, separation of the resulting waste sulfite liquor from the resulting sulfite pulp, and digestion of the sulfite pulp in an alkaline cooking liquor, characterized in that the said alkaline cookingliquor is a solution obtained by concentrating and'smelting, ina reducing atmosphere, the waste liquor from a collateral sulfate process of making pulp, dissolving the resulting smelt in water, and treating the resulting solution with caustic lime.

In testimony whereof, I atlix my signature. DONALD B. BRADNER. 

